A 12V battery that’s dead every morning usually means a module won’t go to sleep. Here’s how to test it, what to fix first, and whether it’s safe to drive.
The usual suspects on an i4
If you're coming out to your BMW i4 with a 12V battery that's flat after a long night, you're not being unreasonable thinking something is running when it shouldn't. The high-voltage battery isn't moving, but the car's control modules are constantly listening—for key signals, for software updates, for the remote app. When they stay awake too long, they quietly drain the small auxiliary battery, and that's the classic parasitic draw. On the i4, the usual triggers include:
- The telematics/connected drive control unit (TCB/ATM) staying powered up or failing to go to sleep
- A comfort access door handle sensor that's intermittently waking the bus
- An alarm system or interior protection module that's hunting
- Aftermarket parts – dashcams, GPS trackers, or phone chargers wired into a "live" circuit
- Software bugs in the sleep/wake logic, fixed by a firmware update
